Dilatation catheters are used to dilate various constricted or obstructed regions in the human body. For example, among the more common dilatation procedures is that involving angioplasty, in which a stenosed region of an artery is forcibly dilated by a balloon mounted on the distal end of the catheter. Such arterial stenoses typically are formed by plaque deposited on or in the arterial wall.
A number of types of dilatation catheters are used in angioplasty procedures. Among the most common is that referred to as an over-the-wire catheter, in which :he catheter is used together with a guidewire. The guidewire is steerable and of a small diameter (such as disclosed in U.S. Pat. No. 4,545,390 to Leary) so that it can be navigated and advanced through the branches and curves of the patient's artery to the site of the stenosis. The guidewire specifically is advanced through the stenosis, thereby providing a path through the patient's arteries by which the catheter can be guided directly to the stenosis. Once the guidewire is placed, the over-the-wire catheter, which has a lumen receptive to the guidewire, is advanced along the guidewire to the site of the stenosis. The guidewire is pushed along the guidewire to locate its dilatation balloon (in collapsed low profile configuration) into the stenosis. The balloon so positioned, then is inflated with a liquid under pressure and for a duration sufficient to affect the dilatation of the stenosis.
Among the difficulties encountered in balloon dilatation of strictures in body lumens, such as dilatation of stenoses in angioplasty, is that the stenosis may be too narrow to enable the balloon portion of the dilatation catheter to be inserted into the stenosis. That is the result, in part, of the construction of the shaft of the catheter which necessarily is flexible so that it can be advanced along the various curves of the patient's vascular anatomy. Consequently, the column strength of the catheter may not be sufficient to enable the catheter to be pushed through the stenosis. Under those circumstances, other approaches may be required in order to treat the stenosis. Typically, the other approaches may involve the use of another catheter having a smaller profile that may be used to predilate the stenosis to enlarge the opening sufficiently to enable the larger, conventional size dilatation catheter to be inserted into the stenosis. For example, such devices are described in U.S. Pat. Nos. 5,102,390 and 4,846,174. The use of such devices may add to the duration and complexity of the dilatation procedure.
It is among the general objects to provide a catheter and guidewire combination to enhance the ability to pass the dilatation catheter.